1. Field of the Invention
The invention relates to a process for the preparation of polyesters of improved dye affinity by reacting dicarboxylic acids or their reactive derivatives with a mixture of diols, consisting of a predominant amount of an alkylene glycol and, a smaller amount of a polyoxyalkylene ether with two free hydroxyl groups on the starter alcohol.
2. Description of the Prior Art
Polyesters, especially those of terephthalic acid or its dimethyl ester and aklylene glycols with 2 to 10 carbon atoms, are outstandingly suitable for the preparation of fibers. These polyesters are relatively insoluble, chemically inactive, hydrophobic materials. However, these properties cause difficulties when fibers or textile products made from them are dyed. Moreover, adsorption and penetration of the dyes into the fibers are made difficult owing to the fact that the molecules are aligned in a stretched state along the fiber axis and are present in a tightly packed form. To overcome these difficulties during dyeing, the dyeing process is carried out either in the presence of carriers at about 95.degree. C. or according to a high-temperature process at 110.degree. C. to 130.degree. C. in pressure-dyeing equipment. The necessary removal of the carriers after dyeing, however, leads to undesirable contamination of the environment, and the thermal stress to a possible lowering in the mechanical properties and thermal stability of the fibers. Moreover, it is usually impossible to achieve a sufficiently uniform dyeing.
U.S. Pat. No. 3,684,768 discloses a fiber-forming polyester that can be dyed with dispersion dyes, and which is synthesized from dialkylene glycol and terephthalic acid containing 0.25 to 10 mole percent of a modifying agent, based on the recurring polyester unit, of a comonomer having the formula ##STR2## in which G represents the --(CH.sub.2).sub.2 -- or the --(CH.sub.2).sub.3 group or a mixture of these groups. R is an alkyl group with 8 to 12 carbon atoms on the average and x has an average value of 8 to 20. In fiber form, the polyesters, so modified, exhibit, for example, increased thermal stability and improved dye affinity. However, the improvement in dye affinity achieved is still insufficient for practical purposes, so that a need still existed for a modifying agent to provide a satisfactory improvement in dye affinity.